DE2331832A1 - ARRANGEMENT FOR SUPPLYING INDUCTIVE AC CONSUMERS - Google Patents

Description

BHOWN, BOVERI & CIE · AKTIENGESELLSCHAFT [ _y J [)

MANNHEIM BROWN BGVtHI

Mannheim, May 25, 1973 Mp. No. 578/73 PAT / Ft / MB

Arrangement for supplying inductive AC consumers

The invention relates to an arrangement for supplying inductive AC consumers with an inverter and capacitors, which supply both the reactive power of the AC consumer and the reactive power demand of the inverter.

For the supply of inductive melting and heating systems, inverters are often used because of their high degree of efficiency used. Losses and installation costs are particularly low when the inverter directs the inductive load while avoiding an intermediate transformer. In the case of the generation of the necessary reactive power by a parallel the capacitor connected to the inductive consumer is correct; AC voltage of the inverter and the consumer voltage match, in the case of reactive power generation by a series capacitor if the currents match, the inverter voltage is then generally only a small fraction of the Consumer voltage. Both for the voltage of the consumer and for that of the capacitors for reactive power generation as well as for the alternating voltage of the inverter there are optimal values at which the costs related to the performance of these system parts run through a minimum. This optimal voltage value is for the capacitors and for the consumer around 1.5 - 2 times the optimal voltage of the inverter. It is therefore with the simple series or series; switching of the reactive power capacitor to the consumer not;

i possible for all parts of the system without switching on a trans-!

formators to realize the economically optimal voltage.

409885/0536

In order to avoid this disadvantage, it has already been proposed that when the reactive power capacitors and loads are connected in parallel, the inverter should only be connected in parallel to some of the reactive power capacitors. Usually the '. Capacitor battery made up of two sub-batteries of roughly the same size . which are connected in series. The inverter ι is connected in parallel to one of these partial batteries. If the series connection of the two partial batteries is connected to the inductive consumer, its voltage is about twice as high as that of the inverter. With this arrangement, it is true that approximately the optimal voltage can be achieved for the inverter and the inductive load, but generally not for the capacitors, because a considerable part of the capacitors has exactly the same voltage as the inverter. When capacitors and inductive loads are connected in parallel, it is possible to keep the deviations of the voltages from their optimal values smaller than when all elements are connected in series, but the parallel connection has the further disadvantage that special starting devices are usually required for the inverter to oscillate . These starting devices represent an additional effort and make the systems more complex, which has an unfavorable effect in terms of maintenance and susceptibility to failure.

The object of the invention is therefore to avoid the disadvantages of the known arrangements. In particular, essentially all individual elements can be designed for optimal tension.

According to the invention, this object is achieved in that at the inverter output a first part of capacitors is connected in series with a second circuit of capacitors

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with the AC consumer and a third part are connected directly in parallel to the inverter output.

The second part of the capacitors is designed in such a way that the resulting phase angle between the current and voltage of the parallel connection of the second part of the capacitors with the AC consumer is set to a value that first part ] of the capacitors.

The first part of the capacitors is advantageously; dimensioned so that its current is straight at its desired voltage is as large as the resulting current of the alternating current consumer and the second part connected in parallel to it

j of the capacitors.

! The third part of the capacitors, which is connected directly in parallel to the inverter output, is then advantageously like this dimensioned so that the total current of the inverter rushes ahead of the voltage by a predetermined angular value.

This arrangement makes it possible to use for all elements With the exception of the third part of the capacitors, the optimum ι voltage can be achieved. Since the contribution of this part of the j [Capacitors for total reactive power is only small, it is economically irrelevant that the voltage of the third

ι part of the capacitors corresponds to the voltage of the inverter. Another advantage of the invention is that no starting devices or other additional measures are required to start the inverter.

Based on the drawing, an example according to the embodiment should be shown in more detail explained.

/ «HCI885 / 0536

Ks shows

Fig. 1 shows the arrangement according to the invention and 2 shows a Zedger diagram for the fundamental oscillations of the currents and voltages that are applied to the switching elements of the circuit shown in Fig.

1 include the arrangement shown.

! An inverter 2 is parallel to a direct current source 1 or WR switched, which is constructed in a manner known per se in a bridge circuit of four thyristors 2a. In row with this inverter 2, so in the input is a smoothing choke Lp switched.

At the inverter output now the voltage U ^ and a corresponding 'speaking current Id is. at. The capacitor circuit according to the invention is now arranged in the output. The consumer, which is an inductive alternating current consumer, is symbolized by a parallel connection of an inductance, i.e. a lossless choke L ^ and an effective resistance R ^. A second part of capacitors is connected in parallel to the inductive alternating current consumer L ₁ / R ^, which is denoted by Cp; is. A first part of the capacitors is connected in series with the second part of the capacitors and with the inductive alternating current consumer and is denoted by the reference symbol C>. Parallel to the output, directly parallel to the output and thus in turn also parallel to the first part of the capacitors and to the parallel connection of the second part of the capacitors and the alternating current consumer, a third part of the ion capacitors is provided, which is denoted by the reference symbol C ^. !

! Set voltage values and current values for the individual parts of the

Capacitors should have together with the alternating current consumer is now shown in Fig. 2 in the phasor diagram. U _{1 is} the voltage on the first part C ^ of the capacitors, the voltage U- is the voltage on the second part C ^ of the capacitors

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and ü, the voltage at the third part C, the capacitors, but at the same time this voltage is also the same as the inverter output voltage. The currents belonging to the individual parts are _{labeled L 1} , EI.

The following is not spoken more of a first part, a second part and a third part of the ^'l Kondenaatoren for simplicity, but only by the capacitor C. Capacitor C ₉ and capacitor C ,. Since «triangle of ttp; innuij *> pointer U ₁ , U ,,, U. ₇ results from the wiinschtt η ratios between the voltages at the inductive v / ech:> tilstromverhraucher, which _{is symbolized by the lossless choke L. and the effective resistance R 1} , as well as the equally large j voltage on the capacitor C ₂ on the one hand and the voltage on the I capacitor C ^ on the other hand to the voltage of the inverter j WR. When using conventional thyristors within the AC;

inverter inverter and conventional capacitors and induction coils is used for the ratio k ₂ between load _{voltage U 2} ! and inverter voltage U - > a value between 1.5 and 2 must be selected. Since the voltage across the capacitor Cp with good approximation '> tion sinusoidal iöt, the voltage on capacitor C. due to the caused by the DC smoothing reactor Lp harmonics "of the inverter current stronger harmonics: said supply content, k is the ratio ^ from For the voltage at the capacitor C. and at the inverter WR it is expedient to choose a value slightly smaller than k ₂ , because then the specific load on the capacitor elements, of which both capacitors consist, will be the same.

i I ,. through the capacitor Cx results as the sum of the current j Iy of the inductive load and the current I _{2 of} the capacitor C ₂ . The size of the capacitor current I, and thus the capacitance of the capacitor C, results from the condition that the Strao! Ir ^ of the inverter, which is the sum of the currents 1 _Λ and I, must have a lead by the j angle) f compared to the voltage U ^. The angle Jf ″ results in turn from

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the condition that: the- Qu.itittif. from this V / ink ^ L utid di-t Kn? i: 5 · frequency of * Wf ^ h ^ oLrLchbernpnnnung gr ^; ii «r * al,> di · Fi t- Lv / e t dv- / AiLt der Im V / echifiLrLciifcer V / Tl '/ f rwe> nd-i t tui fhyx'i.-i t.> i -κ η.-jüiu must. ÜauLt are aiLe ίίϋ. ·,; ^ Ί.ιι known as di? (ieaamtbl in ll.t; i ;; t inu: dio on Kondena.atiJi'f G. η, C, and C. aui: 'ub ^c.-i Len h; t :,; / obfi the i5panmiUi ^r. f> 7firhaLtni3se k. and 1;, and the- V / inkeL γ in v / ¹ i Um Ciri.-n. '. t'ri ffel t: e, -ii: can be held » Au 3ΐίΧ du? τ em /> rt < i 1 i?; {: v / ei let liin im IliubL'uk on lf: a fiau wit I .v.haft Lioii τ .; p - iiiun ^ sanordnuru rn favorable, since 5 the 'lriki dfjr . Kondemia \> t -n c un C 1, only / oil of TFII KLE Ls tung, the 5pannung.37 (Th'iLtniajen in dt; i LüschwiukeL f depends rii'dit iagegen votn liLindleiijtun /:!> bi d. iil * des Vf rhi also · ;, This only affects the Orü.3 «of the capacitor Cp. It is therefore possible to use one and the same inverter, which is dimensioned for a certain active power and a certain consumer voltage and which has the capacitors C ₁ and C, already included, can be used to supply various types of inductive loads, only the capacitor Cp is dimensioned accordingly for the respective application rden.

409885/0536

Claims (3)

1. Arrangement for supplying inductive alternating current consumers, ■ it an inverter and capacitors, which both supply the reactive power of the consumer and cover the reactive power requirement of the inverter, whereby in the inverter output a first part of the capacitors in series to a parallel connection of a second part of the capacitors with de »AC consumers and a third part are connected directly in parallel to the output of the inverter, daduxh characterized that the second part (C ₂ ) of the capacitors connected in parallel to the consumer is possessed in such a way that the resulting phase angle between current and voltage of the parallel connection is set to one value which is derived from the desired ratios between the voltage aa consumer (L ^, / R ₁ ), the AC voltage at the inverter (2) and the voltage at the first j Part (C ₁ ) of the capacitors results. i ι 2. Arrangement according to the Anspruh 1 _f, characterized in that; the first part (C *) of the capacitors so beaesseqdst that j at the desired voltage of this part of the capacitors j the current is just as large as the resulting current - 409885/0536 of the consumer (L ₁ / R ₁ ) and the part (C ₂ ) of the capacitors connected directly in parallel to this. 3. Arrangement according to claims 1 and 2, characterized in that the third part of the capacitors! which is parallel to "inverter (2)" is dimensioned so that the total current of the inverter leads the voltage by a certain angular value (γ-). 409885/0536